Field of the Invention
This invention relates to a method of forming a taper leaf for use in a laminated spring by means of rolling a sheet of spring material.
A taper leaf to be used in a laminated spring is formed in such a taper shape that the terminal portion of a flat plate becomes gradually thinner in its vertical thickness toward its tip. According to a conventional method of forming such a taper leaf, a sheet of spring material, generally designated 1, as shown in FIGS. 1 and 2, is first heated and then its terminal portion 1a is rolled for tapering in its vertical thickness direction. According to this method, the shape after the tapering work is such that the material is rolled to spread out in its lateral direction. Therefore, a measure of breadth trimming cutting or a measure of grinding and abrading (implying also shaving and abrading, hereunder being so meant) has to be applied to the parts spreading out in the lateral direction. That is, in FIGS. 1 and 2, the shape of the terminal portion 1a of the sheet of spring material before being rolled for tapering is as indicated by the broken lines. On the other hand, in the condition that the terminal portion 1a has been rolled for tapering in the vertical thickness direction, broad spreading parts 1b are formed in the lateral direction in the taper-rolled portions, as indicated by the solid lines. Inasmuch as this is inconvenient for the next process of piling and binding the respective leaves, these spreading parts have to be removed by means of breadth trimming cutting, trimming, cutting, grinding, abrading, or erasing.
Another known method utilizes compression of the terminal portion 1a prior to performing the rolling for tapering. This method attempts to reduce the required amount of trimming cutting and the required amount of grinding and abrading. As illustrated in FIGS. 3 and 4, this method pushes molds 2 of predetermined shape onto both sides of the material 1 in order to make the terminal portion 1a of the material have a tapered shape. Thus, the size of the spreading parts 1b, which spread out in the lateral direction during rolling for tapering, is reduced. However, with the press compression process, the vertical thickness of the material increases, or as illustrated in FIG. 4, the material 1 curves in an arcuate shape. Thus, spreading in the lateral direction still occurs during the final rolling for tapering. Therefore, edge trimming cutting and grinding and abrading are still required.
Thus, it is required in the conventional method to apply the process of removing the spreading parts 1b after the rolling for tapering in the vertical thickness direction, and, according to positions to be removed, it is required to slice the material 1 very thinly for breadth trimming. However, this process is difficult from a technical viewpoint and is not economical as too much material is wasted. On the other hand, in case of applying the operation of grinding and abrading instead of the operation of breadth trimming cutting, the working time is so long as to present hindrance to the mass production process. Further, since the parts subjected to the above-mentioned operation of breadth trimming cutting or grinding and abrading from edges, an edge rounding operation is required to avoid unfavourable effects on the performance of a spring formed from the parts. Thus, the conventional methods of forming a taper leaf possess various defects.